IGMP is a network protocol used to establish multicast on networks using IPv4. IGMP is an integral part of IP multicast. The role of IGMP is to notify the local router multicast when the host wants to receive multicast traffic for a particular group. So what is IGMP and how does it work? Let’s explore with Chusa.info in the article below!
What is IGMP?
IGMP (Internet Group Management Protocol) is a standard protocol used by the TCP/IP protocol suite when performing dynamic multicasting, which allows a server to notify switches and routers of its multicast group members.
What is Multicasting?
Multicasting is a type of transmission that allows transmission from one source to a selected group of destinations.
Multicast is a telecommunications industry term used to describe how information is sent from one point to another set of points, and is therefore a form of multipoint connection. This technique is used in the network layer. Its advantage is that the message is sent to many participants or to a closed group of users at the same time. In multicasting, the sender only needs to transmit data at the same rate as if there was only one receiver. Multicast is useful if a group of customers requires a common set of data at the same time. Multicast transmission will save bandwidth significantly.
Dynamic multicasting
The configuration of Dynamic multicasting requires a router or layer-3 device capable of handling multicast groups. The layer-3 device uses IGMP (Internet Group Management Protocol) to determine when a client joins or leaves the group, it uses join and leave messages to add and remove clients from the multicast group.
Many layer-2 devices also have IGMP Snooping capabilities. IGMP Snooping allows a layer-2 device to read IGMP traffic between host and router (or Querier), determine when ports join and leave the group, and automatically forward traffic to ports that are participating in the network. the group. The IGMP Querier is capable of sending periodic messages (called IGMP Membership Query) to the Multicast IP address 224.0.0.1 (all hosts are multicast capable) at a specified interval. This allows a layer-3 device to keep track of which port belongs to which multicast group.
Types of IGMP messages
The main purpose behind IGMP is to allow hosts in a subnet to communicate with local multicast routers about their intent to receive traffic sent to a multicast group. There are different types of messages (messages/messages) used to communicate between the multicast router and the multicast client:
– IGMP General Membership Query (MQ) messages : These messages are sent by local multicast routers to subnets to determine which multicast groups the multicast clients in the network want to subscribe to.
– IGMP Group-specific Multicast Query (MQ) messages : These messages are sent to a specific multicast group address as the destination IPv4 address. These messages are used to identify the members of a particular multicast group.
– IGMP Group-and-source-specific Multicast Query (MQ) messages : These messages are used by multicast routers to find any computer that wants to receive messages from a multicast group with a specific source list.
– IGMP Membership Report messages : These messages are sent by multicast clients inside the subnet to the router to announce the intention to join the multicast group or in response to the Member Query (MQ) message sent by the router.
– IGMP Leave Group (LG) messages : These messages are sent by multicast clients to local multicast routers to notify them that it is no longer interested in traffic from a particular group.
How the IGMP protocol works
When multicast transmission begins, the software or service creates a multicast group. This group address consists of an IP address with the first octet in the range 224 – 239 (Class D) and is specified in the IP packet as the destination address for this traffic. The transmitting server sends a message (called an IGMP Membership Report) to address 224.0.0.2 (all multicast routers) specifying the multicast group address. The switch that receives this message adds the multicast group to the table and adds the receiving port as a member of the group.
It also forwards this report to any other multicast routers. The router then adds these hosts to the multicast routing table. All machines that want to be part of the group also send join messages. The switch intercepts these messages and adds the receiving ports as members of the group. The switch also forwards these messages to the multicast router. All traffic sent to the multicast destination address is forwarded only to the ports participating in the specified group. To keep current membership information, IGMP querier continues to send Membership Queries. All servers that want to stay in the group must answer these queries. If the hosts in the group do not respond within a specified amount of time, the switch will remove those ports from the group table. When all members have left the multicast group, the switch removes the multicast address from its table.
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